Cylinder intake and exhaust events of internal combustion engines may be controlled via poppet valves positioned within the intake and exhaust ports of a cylinder. These poppet valves can be opened by mechanical force provided by cam lobes of a camshaft. The valves close when the valves, or extensions from the valves (e.g., a tappet), encounter a base circle portion of the camshaft. A valve may close due to spring force from a valve spring coupled to the valve stem. Hydraulic dampening mechanisms are often present to reduce noise and wear to the valvetrain components due to higher valve closing forces. Such dampening mechanisms can include an oil-filled chamber housing the valve stem to provide pressure against the closing force of the valve and to softly seat the valve.
The inventor herein has recognized a number of issues with the above approach. The required static spring forces may be greater than the minimum force to close the valve since spring oscillations and pressure forces due to cylinder head port pressures may reduce the force applied to close the valve. As a result, the valve may remain open when it is intended to be closed. Increasing spring forces to counteract cylinder port pressures can lead to additional problems, however. In engines which require high RPM capability, the spring forces may be selected higher to control the dynamic forces which increase with the square of the angular velocity. These higher spring forces may cause increased and unnecessary driving torques during normal, lower RPM operating range. As a result, fuel economy and component durability may be compromised. Additionally, for engines which require higher port pressures in either the inlet or exhaust port due to forced induction, the spring forces may be higher yet so as to counteract the higher port pressures and close the valve. Higher spring forces can cause increased and unnecessary driving torques in the low load, low pressure region of the engine operating range. Thus, engine efficiency benefits provided via engine boosting may be offset by some extent when higher spring forces are applied to close poppet valves.
In one example, the above issues may be at least partially addressed by a valve system for an engine, comprising a first tappet bore of a first cylinder and a second tappet bore of a second cylinder, and a bidirectional oil passage in fluid communication with the first tappet bore and the second tappet bore.
In this manner, oil may flow within the bidirectional oil passage between the first and second tappet bores to provide additional closing force to valves in the tappet bores. For example, the first and second cylinders may be a multiple of 180 crankshaft degrees apart in a firing order of the engine. As a result, as a first valve within the first tappet bore opens, a second valve within the second tappet bore closes. Oil may flow through the bidirectional oil passage from the first tappet bore as the first valve opens, to the second tappet bore. The increased oil in the second tappet bore may provide a closing force to close the second valve. The present disclosure may provide several advantages. Specifically, by providing additional closing force via a bidirectional oil passage, the spring forces required for valve closing may be lowered, thereby improving fuel economy and component durability in certain engine operating conditions. Additionally, the oil in the tappet bores may provide a dampening mechanism to softly seat the closing valve and improve component durability. Further, since oil pressure force within the tappet increases with engine speed, higher valve closing forces may be provided at higher engine speeds when higher valve closing forces may be desirable.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.